A dick-and-ditch is a crude and vulgar term that means to have sexual relations with the intent of never seeing or interacting with the person again in the future. Other terms that mean the same thing are one-night stand, hit and run, and fuck and flee, the latter which was turned into a nice Liz Phair tune.
The term is most typically used when males are talking amongst themselves about sexual conquests. The term probably dates back to the neanderthal days when they would mate with homo sapiens without any intent on moving into the cave with them. Folks who use the term tend to be jerks and users of others (particularly women).
Overall, it's not a nice thing to do unless both parties go into the arrangement with the same outcome in mind, clarifying things with a discussion before sexy time starts.
Iron Noder 2017